Theoretical Study On Nonlinear Laser Ultrasound For Diagnosis Of Early Tooth Microcracks

Cracked tooth has always been the research hotspot and difficulty in oral clinical inspection field due to its shallow depth.There is no effective method in clinical testing to detect it.Compared with the existing diagnostic techniques,laser ultrasonic technology has the advantages of non-contact,no stimulation,fast detection speed and so on.It has huge application prospects.in the field of oral clinical testing.In this paper,a new theoretical model is proposed for the detection of cracked tooth which is based on the theory of nonlinear ultrasound for the tiny width and depth of dental cracks.The surface acoustic waves is generated in the tooth.At the same time using the controllable mechanical wave with the lower frequency,wave magnitude of nm,modulates the crack on the tooth.Using the controllable mechanical wave to control the motion of microcracks,and the nonlinear effect is produced Based on this detection mechanism,a theoretical model is established to characterize the nonlinear modulation of acoustic wave when the motion of the crack wall is composed of a series of spring particles connected by a substrate.Based on the above theoretical model,the influence of the frequency of the modulated wave on the transmission surface acoustic waves in the case of microcracks is studied under the condition that the center frequency of the excited broadband ultrasound is invariable.It provides the theoretical basis for the modulation wave selectionThe microcracks of the teeth is modulated,the transmitted surface acoustic wave signals at different propagation distances is analyzed,and the location of cracks was judged.Based on the theory of beam aliasing,makes the definition of nonlinear parameters.The transmission acoustic signals of various crack depth is analyzed from the time domain and frequency domain.The effects of the transmission components of surface wave are discussed with the changing crack depth.The nonlinear parameters changes along with the depth of the crack.Based on this,the crack depth range was evaluated.